1. Field of the Invention
The present invention relates to a method for deposition of a refractory metal nitride such as titanium nitride, tungsten nitride and molybdenum nitride which are used for preventing diffusion of an interconnection material such as Al or W into a semiconductor layer and as a preventive film for interconnection and, more particularly, to a method for forming a conductive film having a layer of such refractory metal nitride.
Lately, it has been demanded to implement fabrication of semiconductor devices of higher density integration as well as provision of a thinner diffusion layer in semiconductor substrates and multilevel interconnection. Therefore, a barrier metal made of a refractory metal nitride has been used as a base layer or a surface layer of an electrode to prevent intrusion of an electrode metal into the diffusion layer and formation of hillocks on the electrodes and improve adhesion of the electrodes.
2. Description of the Related Art
For forming a barrier metal which serves as a base of a interconnection layer, a Thermal Chemical Vapor Deposition (hereafter referred to as the "thermal CVD") method using halide gas and ammonia gas is widely examined.
For depositing titanium nitride, which will serve as a barrier metal, by the thermal CVD method using, for example, titanium chloride (TiCl4) and ammonia (NH3) are used as a reactive gas, the deposition temperature at which a satisfactory step coverage is obtained is 650.degree. C. or over. In this case, chlorine remaining in the barrier metal is a cause of high resistance and a deposition temperature higher than 600.degree. C. is required to remove chlorine. The details of the above description are disclosed, for example, in the following three documents.
[1] M. J. Buiting, A. F. Otterloo, and A. H. Montree, J. Electrochem. Soc., Vol. 138, No.2, Feb. 1991,
[2] Ivo J. Raaijmakers and Artbur Sherman, Proceedings of the 7th international IEEE V.M.I.C. Santa Clara, June 1990,
[3] E. O. Travis, W. M. Paulson, F. Pintchovski, B. Boeck, L. C. Parillo, M. L. Kottke, K. Y. Yu, M. J. Rice, J. B. Price, and E. C. Eichman, IEEE IEDM Tech. Dig., 47(1990).
A reaction as given below may be caused with TiCl4 and NH3 even at room temperature.
TiCl4+NH3.fwdarw.[TiCl4]n[NH3] (It was described in [1].)
Moreover, at high temperature, the following reaction is occured. EQU TiCl4+NH3.fwdarw.TiN+N2+HCl EQU NH3+HCl.fwdarw.NH4Cl
Both NH4Cl and [TiCl4]n[NH3] remain solid at room temperature and, when they deposit on an internal wall of a chamber, they may be a cause of particles. The internal wall of the chamber of the CVD apparatus should be heated to 120.degree. C. or over to sublimate these particulates. However, if a chamber heating mechanism is provided, the CVD apparatus will be required to be large-sized and power consumption will also increase.
On the other hand, another method is available which uses TiCl4 and N2 as reaction gases and deposits titanium nitride by an Electron Cyclotron Resonance (ECR)--CVD method. In this case, the deposition temperature is raised high. This method of deposition is reported in the document shown below.
[4] Takashi Akahori and Akira Tanihara, Extended Abstracts of the 1991 International Conference on Solid-State Devices and Materials.
However, if a barrier metal consisting of titanium nitride is deposited at such high temperature as described above, there may be caused a melting and hillock of aluminium.
A further another method is also available which allows deposition of titanium nitride at a deposition temperature of 450.degree. C. or under by the thermal CVD method or the photo-assisted CVD method using an organic titanium source. However, a barrier metal made of titanium nitride obtained by this method is inferior in the step coverage and has a high resistance. This is disclosed in the following document.
[5] Ivo J. Raaijmakers, Raymond N. Vrtis, G. S. Sandhu, J. Yang, E. K. Broadbent, D. A. Toberts, and A. Lagendijk, Jun. 9-10, 1992 VMIC Conference.
[6] Kazuya Ishihara, Katsumi Yamazaki, Hideonao Hamada, Koichi Kamisaka and Yasuo Tarui, Japanese Journal of Applied Physics Vol. 29, No.10, Oct. 1990.
[7] Koichi Ikeda, Masahiko Maeda and Yoshinobu Arita, 1990 Symposium on VLSI Technology.
It is known that, when a barrier metal consisting of a refractory metal is directly formed on a semiconductor substrate (or silicon wafer), satisfactory contact between the barrier metal and the semiconductor substrate [8] is not obtained and a contact metal for reducing a contact resistance should be interposed therebetween. After forming the contact metal such as Ti or Al, a natural oxide film should be removed.
[8] C. Y. Ting and M. Wittmer, Thin Solid Films, 96(1982)327-345 Electronics and Optics.
Currently, a contact metal is formed using a sputtering apparatus after the natural oxide film has been removed with a mixed solution of hydrofluoric acid and pure water, then a barrier metal is formed by using the CVD apparatus. Thus, a semiconductor wafer is exposed to the air in each of different processes and the substrate is moved. Since there is unavailable a technology for carrying out the series of these processes without cancelling a vacuum condition, a natural oxide film is not completely removed during formation of the contact metal and faulty contact is prone to occur.